Continuous subcutaneous delivery of medication or monitoring of a body analyte is often accomplished by the use of a cannula or a sensor, which generally remains in place for several days, hereinafter referred to as a “cannula”. Diabetes patients may use such cannula positioned in a subcutaneous compartment for continuous delivery of insulin using pumps and/or for monitoring interstitial glucose levels by sensors. A combination of a tube, connecting an insulin pump to the cannula and a detachable connector is often referred to as an infusion set. Such infusion sets and modes of their insertion are disclosed, for example, in U.S. Pat. Nos. 4,755,173, 5,176,662 and 5,257,980, the disclosures of which are incorporated herein by reference in their entireties. Subcutaneous cannula insertion modes for continuous glucose monitoring are disclosed, for example, in U.S. Pat. Nos. 5,390,671, 5,568,806 and 5,586,553, the disclosures of which are incorporated herein by reference in their entireties.
Usually trans-cutaneous (“hypodermic”) cannula insertion is carried out with a sharp metallic “penetrating member”, which is withdrawn after piercing the skin. The hypodermic insertion is usually painful and requires considerable skill. Some patients are reluctant or hesitant to pierce their own skin, and thus encounter difficulties in proper cannula insertion. Such difficulties can be attributable to insufficient manual dexterity or alternatively to anxiety associated with anticipated discomfort as the needle pierces the skin. This problem can be especially significant when an insulin pump is used since misplacement of a cannula can cause kinking, incorrect insertion angle or incorrect cannula insertion depth leading eventually to cannula obstruction. Consequently delivery of insulin may be hampered thereby creating a life-threatening situation.
In an attempt to cope with this problem, automatic infusion set insertion devices (“inserters”) were developed to assure correct placement of a cannula in the body, at a correct angle, while minimizing hazardous obstructions associated with cannula insertion. U.S. Pat. Nos. 6,093,172 and 6,830,562 disclose inserters comprising a spring-loaded mechanism for an automatic subcutaneous placement of infusion sets. These automatic inserters can be used with so-called “pager-like” pumps having long tubing, cannula and adhesive, altogether constituting an “infusion set”. A new generation of portable infusion devices is the skin adherable pump which has no tubing, as for example disclosed in U.S. Pat. No. 6,699,218. After attaching the device to the user's skin a spring loaded cannula automatically emerges from the device's housing and pierces the skin. Unfortunately, neither an automatic inserter for a pager-like pump infusion set nor automatic insertion mode of a cannula emerging from a skin adherable pump employ a means for reducing the pain associated with skin piercing during cannula insertion.
Continuous glucose monitors are disclosed in U.S. Pat. Nos. 5,390,671 and 6,143,164, assigned to MiniMed and E. Heller & Company, respectively. These devices monitor glucose levels in the subcutaneous compartment by a sensor that is inserted manually or automatically as disclosed in U.S. Pat. No. 7,110,803, assigned to DexCom, in the same manner as a cannula for drug delivery. The above continuous glucose monitors, however, have no means for reducing the pain induced by skin piercing.
Thus, it would be desirable if a subcutaneous cannula, or a sensor, that is associated to a fluid delivery and/or analyte sensing device could be inserted in a precise and user-friendly manner as well as with minimal pain induced by skin piercing.
Pain is defined as an unpleasant sensation and emotional experience arising from actual or potential tissue damage. Undoubtedly, pain is an unpleasant sensation which we instinctively try to avoid. Injection and skin pricking during cannula insertion causes pain and discomfort to the user, and over the years various methods to reduce injection related pain have been explored. The use of hands is unquestionably the oldest, most universally utilized and probably most appreciated means for relieving pain (Nursing Ethics 1996; 3:165-176. American Journal of Nursing 2001; 101:35-39). Touching, massaging or manipulating areas that are painful, tense or tight has been used widely in homes and in hospitals (Archives of Dermatology 1998; 134(11):1373-1386. Journal of Acute and Critical Care 1999; 28(2):114-122. Journal of Canadian Medical Association 2000; 162(13):1815-1820). The gate control theory, which states that physical pain is not a direct result of activation of pain receptor neurons, but rather, its perception is modulated by interaction between different neurons, provides a framework for the mechanism of pain relief. C fibers, which conduct impulses responsible for provoking markedly unpleasant sensations, are inhibited at the dorsal horn of the spinal cord by input from the A delta fibers (Pain: the Science of Suffering Weidenfeld & Nicholson, London 1999). It is suggested that the so-called massage is effective in relieving the pain because of its stimulation of the large-diameter myelinated.
A delta fibers, which thereby increase the inhibitory tone and close the pain gates. Barnhill et al (Journal of Pain and Symptom Management 1996; 12: 52-58) reported that a subject group which received pressure prior to injection demonstrated a significant reduction in perceived pain intensity, and concluded that applying pressure before the injection was useful in reducing pain from an intramuscular injection. Applying pressure to the injection site is believed to increase the stimulation of A delta fibers, resulting in the increase of inhibition of transmission of C fibers by closing the gate. Joanne et al (Journal of Clinical Nursing 2002; 11(4) 457-461) demonstrated a significant difference in the perceived pain intensity for experimental and control conditions. Subjects who were applied with manual pressure before injections reported lower pain intensity scores, whilst those who were not treated with manual pressure before injections reported higher pain intensity scores. Romano & Cecca (Anesth Analg 2004; 99(6):1873. Minerva Anestesiol 2005; 71(10):609-15) showed that tactile stimulation with multiple blunt plastic pins pressed onto the skin at the injection site and during the injection procedure is able to reduce the reported pin prick pain after subcutaneous or intramuscular injection as compared to placebo. Nevertheless none of these mechanical means for pain alleviation is currently employed in cannula insertion devices associated with portable infusion or sensing devices, such as skin adherable infusion/sensing devices or skin adherable insulin pumps that contain a continuous glucose monitor.
Skin cooling is an additional means for reducing pain associated with hypodermic injections (N Engl J Med 1953; 248(16): 692-3. JAMA 1963; 184:319). Various devices and methods are known in the related art for local cooling of skin, for example U.S. Pat. Nos. 2,746,264, 2,982,112, 3,327,713, 3,826,264, 4,614,191, 4,646,735, 5,578,014, and 5,921,963, the disclosures of which are incorporated herein by reference in their entireties. None of these cooling devices for pain alleviation are currently employed in cannula insertion devices associated with portable infusion or sensing devices, such as skin adherable infusion/sensing devices or skin adherable insulin pumps that contain a continuous glucose monitor.
Thus, it is desirable to provide a device capable of being used with portable infusion or sensing devices, e.g., skin adherable infusion and/or sensing devices, and capable of relieving pain associated with inserting a cannula and/or sensor into the body.